When the U.S. Mint introduced special commemorative U.S. silver half dollars and dollars in 1983 and 1984, they were sold individually and as part of Prestige Proof Sets. But most collectors bought their commemorative silver proofs individually. And most proof set buyers continued to acquire regular 5-coin sets each year.
The result is that Prestige proof sets have become BY FAR the scarcest form of these coins. In 1988, 1,359,366 individual Olympic Torches silver dollars were sold and 3,031,287 regular 5-coin proof sets. But only 231,661 Prestige proof sets were issued, containing all six proof coins. That's fewer than 8% of that year's regular proof set mintage!